Defective sheet sorting apparatus



Nov. 7, 1967 D. v. VAN LAANEN 3,351,196

DEFECTIVE SHEET SORTING APPARATUS Filed Nov. 22, 1965 5 Sheets--Sheeil l Nov. 7, 1967 n. v. VAN LAANEN DEFECTIVE SHEET SORTING APPARATUS 5 Sheets-Sheet 2 Filed Nov. 22, 1965 Nov. 7, 1967 D. v. VAN LAANEN 3,351,195

DEFECTIVE SHEET SORTING APPARATUS Filed Nov. 22, 1965 5 Sheets-Sheet 5 Nov. 7, 1967 D. v. VAN LAANEN 3,351,196

DEFECTIVE SHEET SORTING APPARATUS Filed Nov. 22, 1965 5 Sheets-Sheet 4 We@ fw/Www United States Patent Oli 3,351,196 Patented Nov. 7, 1967 ice Filed Nov. 22, 1965, Ser. No. 509,144 2 Claims. (Cl. 209-73) This invention relates to sorting apparatus useful in the separation of relatively large sheets according to the presence or absence of defects therein, and is a continuationin-part of my copending application Ser. No. 190,283, filed Apr. 26, 1962, now U.S. Patent No. 3,219,184.

An object of the invention is to provide, in -apparatus of the character described, a means for feeding sheets of material in a timed continuous high speed stream in which the gap between the trailing and leading edges of the sheets is relatively small, i.e., a matter of a few inches.

The invention will be described in conjunction with an illustrative embodiment in the accompanying drawings, in which- FIG. l is a schematic side elevational View of a portion of the inventive machine;

FIG. 2 is a view similar to FIG. 1 but showing the remaining portion of the machine as the two portions would be mated along the junction line J-J;

FIG. 3 is a fragmentary side elevational view of the sheet stream former or unstacking and shingling mechanism for sheets to be inspected;

FIG. 4 is a fragmentary enlarged sectional view of the lower right-hand portion of FIG. 3;

FIG. 5 is a sectional view such as would be taken from the sight line 5-5 of FIG. 3, and showing the trailing end of the stack of sheets to be inspected;

FIG. 6 is a fragmentary top plan view of a portion of the sheet transfer mechanism, showing the leading edge of the shingled stack of sheets to be inspected;

FIG. 7 is a fragmentary side elevational view of the transfer mechanism seen in FIG. 6 and also showing the entering end of the sheet conveyor;

FIG. 8 is an enlarged fragmentary view of the conveyor portion of the apparatus seen in FIG. 7;

FIG. 9 is a sectional View of the conveyor apparatus seen in FIG. 8;

FIG. 10 is a sectional view such as would be seen along the sight line 10-10 of FIG. 7;

FIG. 11 is a sectional view taken along the sight line 11-11 of FIG. 10;

FIG. 12 is an enlarged fragmentary view of a portion of the apparatus seen in FIG. l1; and

FIG. 13 is a schematic representation of a modified form of a portion of the invention.

In the illustration given, and with particular reference to FIGS. l and 2, the numeral 20 designates a stack of sheets to be inspected and sorted according to whether imperfections are present or not. The present invention has application to especially large sized sheetsof the order of 38 x 5 "--and where the sheets are of cellulosic material, i.e., paper.

Reference to FIG. 1 reveals that the stack 20 is supported on a skid 21 which is carried by an elevator 22. The elevator 22 may be of conventional design, employing chains 22a for feeding the sheets upwardly through suitable electrical controls (not shown) until the topmost sheet comes in contact with a stream former of shingling mechanism generally designated 23.

The result of the operation of the stream former 23 is to advance sheets in shingled fashion toward and into contact with the conveyor generally designated 24 through a transfer mechanism generally designated 25. The conveyor 24 includes a plurality of gripper bars 24a which grip the leading inch or so of the sheet and advance each sheet with the conveyor and in a sequential fashion.

Durmg the course of sheet advancement, the sheets pass through an inspection device generally designated 26. Depending upon the response of the mechanism 26, the sheet will be deposited either in a reject stack 28 or a perfect stack 27. For this purpose, the machine is equipped with a pair of gripper release mechanisms 29 and 30 and a supplemental conveyor generally designated 31.

When a perfect sheet passes by the inspection head, no s1gnal is sent to the gripper release mechanism 29, which then operates to disengage the gripper bars 24a from the sheet, permitting the sheet to flow onto the conveyor 31 and thus into the perfect stack 27. When an imperfection 1s sensed in the sheet by the mechanism 26, the gripper release mechanism 29 is deactivated so as not todisengage or release the gripper bars 24a, and the sheet follows the conveyor 24 until the grippers reach the continually operative release mechanism 30, after which they are deposited in the imperfect stack 28.

The invention will now be described starting from the feed-in end, and, for this purpose, the apparatus may be equipped with a rigid frame, a portion of which is designated by the numeral 32 (see the extreme upper left-hand portions of FIGS. l and 3).

Sheet stream former Referring now to FIG. 3, the numeral 32 designates a lixed frame which supports a floating frame 33, this being achieved through links 34 pivoted at one end on the fixed frame shafts 35 and at the other end upon the floating frame link shafts 36. Thus, the floating frame 33 can describe a portion of an arc about the pivot points defined by the shafts 35.

To unload the paper from the stack 20, the floating frame is equipped with an idler shaft 37 suitably journaled in horizontally adjustable bearings 3S provided as part of the frame 33 (see FIG. 5). Additionally, the frame 33 is equipped with a drive shaft 39 carried in fixed bearings 40. Each of the shafts 39 and 37 are equipped with pulleys 41 (again see FIG. 5) which `optimally may be spaced apart on 8 centers transversely of the machine. The pulleys aligned longitudinally of the machine are connected by mea'ns of perforated bolts 42 so that as the drive shaft 39 rotates, the shaft 37 follows. The frame 33 is equipped with a series of vacuum shoes 42a (see FIGS. 3 and 4) that coact with the perforations 42b in the belts 42 to urge the topmost sheet against the belts 42. The manifold 42C coupled to the shoes 42a for the purpose of communicating the vacuum to the sheet houses a differential pressure switch 42d (see FIG. 5). The switch 42d is set to open the elevator control circuit 2211 controlling motor 22e` (see FIG. 1) whenever a sheet is against the tanning belts 42, thereby stopping further elevator operation.

For the purpose of providing rotation of an intermittent nature for the shaft 39, the shaft 39 is equipped with a one-way clutch 43 (see FIG. 4). The clutch 43 includes a hub 44 and a lever 45. The clutch 43 is so arranged that as the lever 45 is rotated counterclockwise, the drive shaft 39 is rotated, while upon clockwise rotation of the lever 45, the drive shaft 39 is stationary.

To insure that the floating frame, or, more particularly, the belts 42, are in pressure contact with the top or uppermost sheet of the stack 2i), the floating frame is equipped with a reinforcing angle 46. This angle 46 receives the end of an I-bolt 47 as in a bracket 48, with the I-bolt passing through the fixed frame 32. A compression spring 49 is positioned about the I-bolt 47 and compressed between the frame 32 and a nut 50 so as to bias the floating frame 33 downwardly.

Sheet transfer mechanism Referring now to FIG. 7, it will be seen that at the leading or forward end of the stack 20 there is located a feed wheel shaft 51. This may be conveniently supported within frame 32, and the shaft 51 is equipped with feed wheels 52 aligned with the pulleys 41 (compare FIGS. 5 and 6). Optirnally, the outer periphery of the wheels 52 are of polished, chrome-plated steel into which are set segments of rubber 52a and which extend radially slightly beyond the polished diameter of the wheel. To the end of the feed wheel shaft 51 is fitted a T-slotted ange 53, into which a T-head bolt 54 is tted. A connecting rod 55 is connected to the bolt 54 and lalso to the lever 45 as at 56 (see FIG. 4).

The connecting rod serves to translate the rotary motion of the shaft 51 into reciprocating motion of lever 45, which in turn imparts an intermittent rotary motion to the shaft 39. This results that in each revolution of the feed wheel shaft 51, a movement of a successive top sheet toward the feed wheels 52 will be achieved. Further, it will be seen that such revolutions of the feed wheel shaft S1 will result in a number of the top sheets being fed forwardly ina shingled or fanned sequence.

Located at the top of the stack 20 and parallel with the sides of the stack are side guide plates 57 (See FIG. 6) which are mounted as part of the iixed support frame 32 and which are adjustable to stack width. As such, the guide plates 57 guide the shingled top sheets toward the feed wheels 52.

Located near the leading end of the stack 20 and coinciding vertically with the top of the stack 20, are sets of air blast nozzles 58 so oriented as to blow a stream of air horizontally across the top of the stack at about 45 to the line of sheet travel. The air blast thus separates the top leading sheets of the shngled stream and oats them sequentially on an air layer in readiness for feeding.

Located beneath the feed wheels 52 is a feed board 59 which is provided ,as part of frame 32 (see FIG. 7). It is upon the feed board 59 that the successive leading sheets of the shingled stream are supported. Through slots in the board which are located directly in line with the feed wheels 5 2, retarding blocks 60 are extended toward the feed wheels. The blocks 60 may be advantageously constructed of Carborundum and are fixed to lead springs 61 which are biased downwardly against an adjusting screw 6 3 mounted in bracket62 (again see FIG. 7).

The speed of the feed wheels 52 is such that the wheels make one revolution for each passage of ,a gripper bar 24a. The radial timing of the feed wheels is such that the leading edge of the rubber segment 52a arrived at the nip of the wheel and retarding block at the same instant that the trailing edge of the prior fed sheet leaves that location. The next sheet to be fed from the top of he stack at this instant has now been advanced beyond the grip of the fanning belt 42, 'and is supported by the feed board 59 and by the air cushion provided by the nozzles 58. However, this referred-to next sheet is held from further forward motion by the retarding blocks 60.

Continued rotation of the feed wheels creates a nip pressure between the rubber segments and the retarding blocks, advancing the top sheet forward to the point at which it is grasped on its leading edge by the gripper bars 24a. By the time the top sheet is fed by the amount of the peripheral length of the rubber segment 52a, a gap will exist between the leading edge of the fed sheet and the trailing edge of the preceding sheet due to the higher velocity of the conveyor 24. 'Into this gap, the next gripper bar. 24a enters to grasp and carry the fed sheet forward, while the succeeding sheet is. retarded between the retarding blocks 60 and the polished periphery of the feed wheels S2. The operation of this portion of the apparatus results in a steady, high speed flow of sheets of material just sufliciently spaced apart for gripping by the gripper bar 24a. The nature of the feeding mechanism allows the very thin, large sheets to be fed at speeds far beyond conventional stream feeders presently known, the speeds achievable herein being of the order of 1000 feet per minute.

Conveyor The apparatus for advancing the sheets sequentially past the inspection device 26 will now be described, and with particular reference to FIGS. 7-12, the third and i fourth drawing sheets.

First referring to FIG. 7, it will be seen that the coni veyor 24 includes a tail sprocket 64. The sprocket 64 is rotatably mounted on a tail shaft by a bearing 64a (see FIG. l0). It will be appreciated that a pair of 32. From FIG. l0, it will be seen that the frame portion 69 also supports tail shaft 65.

Each chain 66 also carries brackets 71 for supporting the gripper bars 24a. Extending between opposite aligned gripper brackets 71 are gripper bar shafts 72 and 73 (see FIG. 11). As can be appreciated from a consideration of FIG. 9, the gripper bars 24a pivot with the first gripper bar shaft 72 into engagement with blocks 74 supported between the first and second shafts 72 and 73 so as t0 grip the leading edge of a sheet S.

To achieve this pivoting motion, the gripper bar shafts 72 are equipped. with cam followers 75 (see FIG. 7)

which engage cams 76 rigidly mounted on the tail shaft 65. The cams '76 thus overcome the urging of the coiled springs 77 which normally urge the gripper bars or head 24a into engagement with the anvil blocks 74.y

In operation, the contour of the cam 76 develops a snap closing action on the gripper bars 24a just as the grippers pass by the feed board or plate 59. Thereafter, with the gripper bars 24a being urged against the anvil blocks 74, the sheets are sequentially carried past the inspection mechanism 26 and to the release mechanism 29 and 30.

Inspection head rather than to the perfect stack 27. As the sheet enters` the inspection head 26, it passes through an anti-flutter device generally designated 78, wherein a suction head 79 is mounted over an air jet 80. The device 7S, by forcing the sheet up against the suction head, exerts just enough drag or tension on the sheet to keep it from fluttering during the critical inspection instant.

Inspection sheet transport mechanism Mounted forward of the release point and extending back into the release area, is a set of stripper fingers 81. These are so spaced and situated that they extend over the gripper bar as it changes line of travel, and between the segmented portions of the gripper bar. The stripper fingers 81 act to assure positive release of the sheets from the gripper bar 24a, and further to guide the sheets in a level plane as they progress beyond the release point. Mounted above the stripperlingers 81is a belt mechanism generally designated 82, which is synchronized to operate at a speed equal to or slightly greater than the conveyor 24.. `Air jets from beneaththe stripper fingers as at 83 force the sheet upward against the belt 82, thus creating enough pressure to drive the sheet forward over the stripper fingers 81.

A second belt mechanism generally designated 84 supports the sheet from beneath after it has passed beyond the stripper fingers. This belt mechanism and the one above it, i.e., 82, serve to carry the released sheet clear of the release area.

The perfect sheet drops from the high speed parallel belt mechanism 82 and 84 onto a slower-moving belt 85 in such a manner that the sheets are overlapped upon each other, or shingled. The slow-down belt 85 then carries the overlapped stream of perfect sheets and into the stacking apparatus of layboy 27, where jogging anms and air jets (not shown) combine to build a pile of perfect sheets. `It will be appreciated that the slow-down belt 85 is interconnected with the circuitry of the inspection mechanism 26 and the gripper release mechanism 29, so that the slow-down belt 85 is stopped when defective sheets are by-passed beyond the release point for perfect sheets. Otherwise, passage of defective sheets would cause gaps in the overlapped stream and thus interfere with the stacking operation of the perfect sheets. Facilitating the transfer of the sheet from the high speed belts 82 and 84 to the slow speed belt 85 and its companion belt 86 is an air float mechanism 87 (see FIG. 2).

A similar arrangement of stripper fingers 88 and belts 89 and 90 is provided for the defective sheets, and it will be appreciated that if further refinement is desired, separation of the sheets into various degrees of imperfection may be utilized by reproducing the various individual structures presented herein for the two-way separation.

As a defective sheet is carried past the release mechanism 29, the line of travel of conveyor 24 changes and drops downward t put the gripper bars 24a beneath the release point. To assist in putting the defective sheet into this new plane, a vacuum roll 91 may be employed. Suction thus causes the sheet to wrap partially around this roll. Air jets 92 may be used to force the sheet against the vacuum roll at the point of initial contact. The wrap thus created is sufficient to keep the otherwise unsupported sheet from whipping as it is carried into a new line of travel. The defective sheet is released when the cam follower 75 strikes the cam 30, after which the procedure for transporting the defective sheets is the same as that discussed hereinabove relative to the perfect sheets.

Operation In the operation of the machine, the length of the sheet will govern the number of gripper bars 24a used and the length of the chain. Also, the length of the sheet governs the adjustment of the connecting rod stroke (its eccentricity at the feed wheel). The length of the sheet further governs the setting of the jogging arms and stops (not shown) at the perfect sheet layboy and reject piler.

The width of the sheet governs the following factors: (l) transverse setting of feed belts and wheels; (2) adjustment of side guides at feed end; (3) adjustment of jogging arms and guides at perfect sheet layboy and at reject piler; (4) location of air blast nozzles at feed end; (5) location of air jets at release point for perfect paper; (6) number of photocell units operative in inspection head; and (7) location of inspection head in transverse direction to line of sheet travel.

The length and thickness of the sheet govern the speed of the slow-down tapes (for the amount of overlap) at the release for perfect sheets. The thickness and type of sheet govern the adjustment of the fanning belt 42 and its pressure on the stack at the feed end as well as the adjustment of the leaf spring setting for gap between retarding block and feed wheels.

The width, length, thickness and type of sheet govern the air pressure setting at the feed end air nozzles, at the anti-fiutter device, and at the release points.

The initial step is to place a supply of paper to be sorted onto the skid 21, the elevator chains 23a being hung sufficiently out of the way for side entry of a loaded skid of sheets. The chains operate through electrical controls 22b and 22C to elevate the paper until the paper cornes into contact with the fanning belt 42.. Thereafter, the main drive is started, andthe feed assembly, conveyor assembly, and receiving assembly move in synchronized fashion. At the same time, the inspection head is energized.

With the differential pressure switch 42d installed in the vacuum manifold 42C which supplies the vacuum shoes 42a within the fanning belts 42, the switch 42d is set to open the elevator control circuit 22b whenever a sheet is against the fanning belts 42 and thus closes the ports of the vacuum shoes 42a above the perforated belts 42. This serves to control substantially exactly the level of the input pile at proper feeding heights. Since there is no downward pressing fingers or pawls, the sheet is free to be lifted by the air blast from the nozzles 58 up into the vacuumized fanning belts 42.

Immediately upon contact o-f a sheet against the belts, the ports within the vacuumized shoes are closed, causing vacuum pressure in the vacuum manifold 42o to rise. This rise in vacuum in turn opens the differential pressure switch 42d within the manifold 42C, breaking the electrical circuit of the elevator 22 and causing the elevator 22 to stop rising.

Conversely, when enough sheets have been fed from the pile by the fanning belts 42, the pile height falls to a point at which the air blast no longer puts the top sheet into contact with the vacuumized fanning belts 42. Then the vacuum ports in the shoes 42a are open to atmosphere, pressure in the vacuum manifold is lowered, causing the differential pressure switch 42d to close. This in turn energizes the electric circuit of the elevator 22, causing the elevator to rise to proper level.

Rotation of the feed wheel shaft 51 and consequent rotation of fanning belts through connecting rod 55 and clutch 43 creates an overlapped stream of paper which moves forward until the leading sheet meets the retarding blocks 60. The retarding blocks 60 momentarily interrupt the forward progress of the leading sheet until the revolution of the feed wheels 52 brings the rubber segment 52a into contact with a sheet. Continued rotation of the feed wheels 52 creates nip pressure between the rubber segment 52a and the retarding blocks 6i), thus driving the top sheet forward in timed relation, synchronized with the arrival of the gripper bar 24a. The top sheet being fed through the nip meets an arresting gate 93, which positions the leading edge for grasp by the gripper bar 24a.

The gripper bar 24a being carried by the sheet conveyor 24 arrives at the pick-up point with the bar heads 24a raised open above the anvil blocks 74 due to the action of cam 76, cam follower 75, and the gripper bar spring mechanism 77. Continued travel of the gripper bar 24a and subsequent action of cam follower '75 and gripper bar spring 77 brings the grippers do-wn over the leading edge of the sheet and into contact with the anvil block 74. The speed of the conveyor 24 is such that the entire length of one sheet is pulled over the retarding blocks 60 before the feed wheels 52 complete revolution and the rubber segments 52a again arrive at the feed position. The sheet thus gripped is advanced with the conveyor 24 through the inspection head 26 for ultimate disposition in a perfect or reject pile.

Referring now to FIG. 13., the numeral 159 designates a feed board and which is adapted to support the sheets from the pile 120 as they come from the fanning belt's' 142. The feed board 159 is equipped with conveyor tapes 192 toI assist in carrying the stream forward to the control feed wheel 152. Along the feed board 159 is seen a photoelectric vreceiver 193 and high intensity light source 194, a stationary vacuum box 195 and a vacuumized and driven forwarding belt 196.

Certain grades of paper sheets, particularly those sheets which have been simultaneously cut from multiple webs, tend to stick together in blocks instead of proceeding individually. In order to achieve optimum speed under such conditions, I rely upon the interaction of the air nozzles 58 and vacuum shoes 42a to create enough separation to allow the belts 42 to forward the topmost sheet. When two or more sheets are fed together in a block, the device shown schematically in FIG. 13 is employed to create positive separation without loss of production speed.

For this purpose, the photoelectric receiver 193 is tuned in relation with the high intensity lamp 194 to accept the beam interruption (loss of light) attendant on the passage of one sheet. However, two or more sheets arriving in the beam together cause the receiver 193 to actuate relay 197. When relay 197 is actuated, it deactivates the clutch 198 controlling the farming belts 42, thus stopping input of more sheets to the feed board 159. Also, when the relay 197 is actuated, it opens solenoid valves 199 and 200 installed, respectively, in the lines 201 and 202 from the vacuum manifold 2.03 to the vacuum box 195 and vacuumized belt assembly 196.

When this occurs, the vacuum box 195 immediately engages the bottommost sheet, while the auxiliary belt assembly 196 engages the topmost sheet. Since the auiliary belt assembly 196 is driven, it will carry the topmost sheet forward over the exposed area of the vacuum box and into the nip of the higher speed feed wheel and retarding block assembly. As the top sheet is carried by the auxiliary vacuum belt assembly 196 across the vacuumized table area, any sheets still attached to the underside of the top sheet are drawn downwardly by the vacuum box 195 and held to the table by the vacuum box 195. Thus, the topmost sheet arrives at the juncture of the high speedfeed wheel 152 and retarding block 160 clearly separated from any previously attached sheets. The grasp achieved by the high speed feed wheel 152 and the retarding block 160 on the topmost sheet is suicient to overcome the hold on the sheet of the auxiliary vacuum belt 196.

Further, I provide suficient spacing between the high speed feed wheel 152 and the high intensity light beam 194 so that in normal operation the top sheet of a stream is removed from under the light 194 by the feed wheel 152 before the leading edge of the next succeeding sheet breaks the beam. Thus, the entire system of feeder and conveyor and sorter can operate without interruption as long as the proper sheet separation is achieved by the tanning belts 142. However, when proper separation does not occur, the arrangement of FIG. 13 takes over to create separation of the grouped or blocked sheets with- 8 out loss of production time and without damage to the sheets.

I claim:

1. In a sorting machine for separating acceptable from unacceptable paper sheets, an elevator for elevating a stack of horizontally disposed, generally rectangular paper sheets, a horizontally elongated frame about said elevator and equipped with a sheet shifter above said elevator for sequentially shifting the sheet uppermost on said stack to provide a sheet edge portion in overlapping relation with the rest of said stack, ,a horizontally disposed gripping conveyor on said frame adapted to grip the leading edge portion of said uppermost sheet to horizontally advance said sheet, feed Wheel means on said frame interposed between one end of said conveyor and said sheet shifter for advancing and controlling said uppermost sheet toward and into said conveyor, sheet inspection means on said frame for simultaneously ascertaining the presence of defects in both sides of said sheet, a pair of receivers, one -for acceptable sheets and one for unacceptable sheets, horizontally .spaced adjacent the other end of said conveyor, and means responsive to a signal from said inspection means for conducting a given sheet to one of said receivers, said sheet shifter comprising a plurality of perforated belts reeved on pulleys,

vacuum shoe means on said `frame and contacting said belts, air blast means horizontally aligned with said uppermost sheet to urge said sheet into engagement with said belts, and pressure sensitive means operatively associated with said vacuum shoe means and said elevator for controlling the action of said elevator as a function of the position of said uppermost sheet relative to said perforated belts.

2. The sorting machine of claim 1 in which sheetsensing means is interposed between said feed wheel means and said sheet shifter, said sheet-sensing means being operative to sense the presence of more than one thickness of sheet and thereupon to deactivate said sheet shifter, and vacuum gripping means operatively associated with said sheet-sensing means for shingling a plurality of sheets sensed by said sensing means.

References Cited UNITED STATES PATENTS 2,393,614 1/1946 Curtis 209-88 2,736,431 2/1956 Coleman et al 209-l1l.7 3,023,900 3/ 1962 Thier 209-71 3,103,355 9/1963 Hubbard et al. 271-12 X M. HENSON WOOD, IR., Primary Examiner.

A. KNOWLES, Assistant Examiner. 

1. IN A SORTING MACHINE FOR SEPARATING ACCEPTABLE FROM UNACCEPTABLE PAPER SHEETS, AN ELEVATOR FOR ELEVATING A STACK OF HORIZONTALLY DISPOSED, GENERALLY RECTANGULAR PAPER SHEETS, A HORIZONTALLY ELONGATED FRAME ABOUT SAID ELEVATOR AND EQUIPPED WITH A SHEET SHIFTER ABOVE SAID ELEVATOR FOR SEQUENTIALLY SHIFTING THE SHEET UPPERMOST ON SAID STACK TO PROVIDE A SHEET EDGE PORTION IN OVERLAPPING RELATION WITH THE REST OF SAID STACK, A HORIZONTALLY DISPOSED GRIPPING CONVEYOR ON SAID FRAME ADAPTED TO GRIP THE LEADING EDGE PORTION OF SAID UPPERMOST SHEET TO HORIZONTALLY ADVANCE SAID SHEET, FEED WHEEL MEANS ON SAID FRAME INTERPOSED BETWEEN ONE END OF SAID CONVEYOR AND SAID SHEET FILTER FOR ADVANCING AND CONTROLLING SAID UPPERMOST SHEET TOWARD AND INTO SAID CONVEYOR, SHEET INSPECTION MEANS ON SAID FRAME FOR SIMULTANEOUSLY ASCERTAINING THE PRESENCE OF DEFECTS IN BOTH SIDES OF SAID SHEET, A PAIR OF RECEIVERS, ONE FOR ACCEPTABLE SHEETS AND ONE FOR UNACCEPTABLE SHEETS, HORIZONTALLY SPACED ADJACENT THE OTHER END OF SAID CONVEYOR, AND MEANS RESPONSIVE TO A SIGNAL FROM SAID INSPECTION MEANS FOR CONDUCTING A GIVEN SHEET TO ONE OF SAID RECEIVERS, SAID SHEET SHIFTER COMPRISING A PLURALITY OF PERFORATED BELTS REEVED ON PULLEYS, VACUUM SHOE MEANS ON SAID FRAME AND CONTACTING SAID BELTS, AIR BLAST MEANS HORIZONTALLY ALIGNED WITH SAID UPPERMOST SHEET TO URGE SAID SHEET INTO ENGAGEMENT WITH SAID BELTS, AND PRESSURE SENSITIVE MEANS OPERATIVELY ASSOCIATED WITH SAID VACUUM SHOE MEANS AND SAID ELEVATOR FOR CONTROLLING THE ACTION OF SAID ELEVATOR AS A FUNCTION OF THE POSITION OF SAID UPPERMOST SHEET RELATIVE TO SAID PERFORATED BELTS. 